1. Field of the Invention
The invention relates to a longitudinally controllable adjustment device, comprising a cylindrical housing closed at one end and filled with a pressure medium, a piston rod sealingly extending from the other end of the housing and slidable therein, a piston disposed in the housing and sealingly guided against an inner wall thereof, the piston being fixedly connected with the piston rod and slidable together with the piston rod and which divides the inner chamber of the housing into two partial chambers, the piston having a receptacle for receiving without play the cylindrical piston rod, a valve passing through the piston and being substantially arranged in a valve housing formed by a bore in the piston rod, for connecting or separating the two partial chambers comprising a valve body passing through the piston and being actuable by means of a trigger pin slidably guided in the piston rod, which valve body has one sealing face which abuts against a seal and which by the trigger pin, can be slidingly brought into a position bridging the seal.
2. The Prior Art
Adjustment devices of the generic type are known in numerous forms, as for example from German Utility Models DE-GM 74 34 098, DE-GM 74 34 102, DE-GM 74 34 101 and DE-GM 86 01 132 (corresponding to Published, Non-Examined European Patent Application EP-OS 0234 184). They are at least partially filled with pressure gas, by means of which the piston rod can be pushed out of the housing or it can be pushed back in against the force of its pressure, when the valve is opened. If the piston itself is slidable in a fluid-filled chamber, then a complete, i.e., for all practical purposes rigid, arrestment of this adjustment device, which can also be called a gas spring, becomes possible. If, however, the entire housing is filled with pressure gas, a spring potential having a very steep distance/force line is possible even with the valve closed. The known adjustment devices have the disadvantage of a very expensive manufacture and assembly of the piston, the piston rod and the valve, with the need of improvement of the guiding and sealing conditions.